Oiling structure for engine

ABSTRACT

A lower cam housing is formed to be a separate body from a cylinder head and the lower cam housing is arranged at a joint surface of the cylinder head, a first upper oil passage reaching from an oil entry passage to the joint surface is formed inside the cylinder head and an upstream end of the first upper oil passage is opened at the joint surface, and a second upper oil passage through which the oil reaches to the joint surface via an upper side than the joint surface is formed in the lower cam housing, where an upstream end of the second upper oil passage is in communication with the oil entry passage side at the joint surface, and a downstream end of the second upper oil passage is in communication with the first upper oil passage at the joint surface.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of priority to JapanesePatent Application No. 2012-207147, filed on Sep. 20, 2012, the entirecontent of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an oiling structure for engine, andmore specifically, to an oiling structure for supplying oil to ahydraulic lash adjuster.

BACKGROUND OF THE INVENTION

In general, in an engine in which the opening and closing of a valve iscarried out by a swinging rocker arm, a plurality of hydraulic lashadjusters (referred hereafter as lash adjusters) are arranged along adirection (a length direction) in which cylinders are arranged. Thislash adjuster is made such that oil is supplied at a prescribed pressurefrom an oil pump arranged at a lower portion of the engine. Then, thelash adjuster has an effect of canceling the valve clearance caused bythe thermal expansion of the valve, for example, by adjusting a positionof the valve by utilizing the oil pressure of the oil during the engineoperation. In the lash adjuster, an oil passage for the oil pumped fromthe oil pump of the engine is passing. The oil passage is formed in thecylinder block and the cylinder head. In the conventional engine, theoil passage formed in the cylinder head such that it is in communicationwith the oil pump side is positioned at a lower position than the oilpassage to the lash adjuster. For this reason, in the conventionalengine, the oil present in the oil passage from the oil pump to the lashadjuster at a time of the engine stop has been such that it flows downto the lower portion side of the engine, via this oil passage.Consequently, in the conventional engine, the sufficient oil is notsupplied to the lash adjuster at a time of the engine re-start, whichbecomes a cause for generating a remaining air inside a hydraulicchamber inside the lash adjuster, and there has been a danger ofadversely affecting the opening and closing of the valve.

As a measure against such a problem, there is known a lubrication devicein which the oil passage provided toward the lash adjuster from thelower portion side of the cylinder head is equipped with an upper oilpassage extending to an upper side than the lash adjuster, and a returnoil passage that returns from this upper oil passage to a lower side andreaches to the lash adjuster (see Japanese Patent ApplicationPublication No. H5-306603, for example). In this lubrication device, theoil supply to the lash adjuster from the return oil passage becomespossible at a time of the engine re-start. In this prior art, the oil issupplied to both the lash adjuster of the intake side (also referred toas the air intake herein) and the lash adjuster of the exhaust side, sothat a communication pipe for making the oil passage of the air intakeside and the oil passage of the exhaust side in communication is addedto a space inside the cylinder head cover. At the both end portions ofthis communication pipe, flanges are provided, and these flanges arefixed to an upper end surface of the cylinder head by bolts.

However, in the above noted prior art, the communication pipe isarranged in a space between the upper end surface of the cylinder headand the cylinder head cover, so that it has been one in which thecommunication pipe is easily oscillated by the vibration of the engine.For this reason, at the flanges of the both end portions of thecommunication pipe, there has been a danger of having the oil flowingout due to the loosening of the bolts. Also, in such a prior art, theassembling work for bolting the communication pipe to the upper endsurface of the cylinder head is cumbersome.

SUMMARY OF THE INVENTION

The present invention is one that has been made in view of the abovenoted problems, and has an object to provide the oiling structure forengine with a high productivity, capable of preventing the outflow ofoil inside a hydraulic lash adjuster after the engine stop, andpreventing the generation of the engine noise (tappet sound) at a timeof the re-start.

In order to solve the above described problems and achieve the object, aform of the present invention is an oiling structure for engine,including a cylinder head of the engine having a cam shaft, a rocker armfor swinging in conjunction with a rotation of the cam shaft, a valvefor carrying out an opening and closing operation in conjunction withthe swinging of the rocker arm, and plural pairs of cam housings formedby lower cam housings and upper cam housings, for sandwiching andaxially supporting the cam shaft to be freely rotatable, wherein one endof the rocker arm is supported to be capable of swinging via a hydrauliclash adjuster, oil ejected from an oil pump is guided to an oil hole ofthe lash adjuster in the cylinder head, and an oil passage for the lashadjuster is formed in the cylinder head at the same height (or at anidentical level) as the oil hole. In addition, at least one of the lowercam housings is formed as a separate body from the cylinder head joinedto the cylinder head at a joint surface (the joint surface can also bereferred to as a joint surface rejoin or region of the joint surfaceherein, referring to the region at which the separate body is joined tothe cylinder head). Further, a first upper oil passage extends from theoil passage for the lash adjuster to the joint surface and is formedinside the cylinder head, and an upstream end of the first upper oilpassage is opened at the joint surface region. An oil entry passage forsupplying the oil ejected from the oil pump is formed inside thecylinder head, and a downstream end of the oil entry passage is openedat the joint surface, and a second upper oil passage through which theoil reaches to the joint surface from above the joint surface is formedin the lower cam housing, where an upstream end of the second upper oilpassage is in communication with the oil entry passage at the jointsurface, and a downstream end of the second upper oil passage is incommunication with the first upper oil passage at the joint surface.

As the above noted form, it is preferable that the oil passage for thelash adjuster comprises an air intake side oil passage for the lashadjuster which is in communication with the lash adjuster that is to beused at an air intake side, and an exhaust side oil passage for the lashadjuster which is in communication with the lash adjuster that is to beused at an exhaust side, and the second upper oil passage is incommunication with each of the first upper oil passage on the air intakeside and the first upper oil passage on the exhaust side.

According to the present invention, it is possible to realize the oilingstructure for engine with a high productivity, capable of preventing theoutflow of oil inside a hydraulic lash adjuster after the engine stop,and preventing the generation of the engine noise (tappet sound) at atime of the re-start.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an engine to which an oiling structure forengine according to an embodiment of the present invention is applied.

FIG. 2 is a plan view showing a state in which a cam shaft (indicated bya virtual line), a lower cam housing and an upper cam housing areassembled to a cylinder head in an engine to which an oiling structurefor engine according to an embodiment of the present invention isapplied.

FIG. 3 is a plan view of a cylinder head in an engine to which an oilingstructure for engine according to an embodiment of the present inventionis applied.

FIG. 4A is a cross sectional view of a lash adjuster.

FIG. 4B is a cross sectional view showing an operation in which aplunger follows a rocker arm in a lash adjuster.

FIG. 5 is a cross sectional view along V-V line in FIG. 2.

FIG. 6 is a cross sectional view along VI-VI line in FIG. 2.

FIG. 7 is a cross sectional view along VII-VII line in FIG. 3.

FIG. 8 is a cross sectional view along VIII-VIII line in FIG. 2.

FIG. 9 is a cross sectional view along IX-IX line in FIG. 5.

FIG. 10A is a plan view of a lower cam housing used in an oilingstructure for engine according to the present embodiment.

FIG. 10B is a front view of a lower cam housing used in an oilingstructure for engine according to the present embodiment.

FIG. 10C is a bottom view of a lower cam housing used in an oilingstructure for engine according to the present embodiment.

FIG. 11A is a front view of an upper cam housing used in an oilingstructure for engine according to the present embodiment.

FIG. 11B is a bottom view of an upper cam housing used in an oilingstructure for engine according to the present embodiment.

FIG. 12 is a perspective view schematically showing an oil entrypassage, an oil passage for a lash adjuster, a first upper oil passage,and a second upper oil passage in an oiling structure for engineaccording to an embodiment of the present invention.

FIG. 13 is an explanatory diagram schematically showing an oil entrypassage, an oil passage for a lash adjuster, a first upper oil passage,and a second upper oil passage in an oiling structure for engineaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following, the detail of the oiling structure for engineaccording to embodiments of the present invention will be describedbased on the drawings.

(Schematic Configuration of an Engine)

As shown in FIG. 1 to FIG. 3, the engine 1 of the present embodiment isequipped with a cylinder block 2, a cylinder head 3 arranged on thecylinder block 2, lower cam housings 4, 4A (see FIG. 3) arranged at anupper portion of the cylinder head 3, an upper cam housing 5 arranged onthe lower cam housing 4, an upper cam housing 5A (see FIG. 2) arrangedon the lower cam housing 4A, a cam shaft 6 on an air intake side, a camshaft 7 on an exhaust side, a cylinder head cover 8 (see FIG. 1)arranged to cover an upper portion of the cylinder head 3, a crank shaft9 axially supported to be freely rotatable at a lower portion of thecylinder block 2, a crank shaft bearing 10 for axially supporting thecrank shaft 9 at the lower portion of the cylinder block 2, an oil pan11 provided at a lower side of the cylinder block 2, and an oil pump 12provided at one end of the crank shaft 9.

As shown in FIG. 2 and FIG. 3, the cylinder block 2 (see FIG. 1) and thecylinder head 3 have, in their interior, a first cylinder formationregion 13 in which a first cylinder 13A (see FIG. 8) is formed, a secondcylinder formation region 14 in which a second cylinder not shown in thefigure is formed, and a third cylinder formation region 15 in which athird cylinder not shown in the figure is formed. As shown in FIG. 8,inside the first cylinder 13A (the second cylinder, the third cylinder),respectively, an up and down moving piston 16 is linked to the crankshaft 9 via a connecting rod 17, such that a reciprocating motion of thepiston 16 is converted into a rotational motion and conveyed.

As shown in FIG. 8, at positions respectively corresponding to the firstcylinder 13A (the second cylinder, the third cylinder) in the cylinderhead 3, air intake valves 20 and exhaust valves 21 for opening andclosing openings in communication with an air intake port 18 and anexhaust port 19 are provided. In the present embodiment, a pair of theair intake valves 20 and a pair of the exhaust valves 21 are provided ateach cylinder. These air intake valves 20 and exhaust valves 21 areprovided to be capable of being moved forward and backward in axialdirections by valve guides 22, and biased in directions for pulling up(valve closing directions) by valve springs 23.

(Rocker Arm)

As shown in FIG. 8, in the present embodiment, to an upper end portionof each of the air intake valve 20 and the exhaust valve 21, a lowerface of one end portion 24A of a rocker arm 24 is arranged to beabutting. The other end portion 24B of this rocker arm 24 is supportedby abutting to a tip end of a plunger 27 of a lash adjuster 25. That is,the rocker arm 24 is supported at the tip end portion of the plunger 27that is to be a swinging center (a pivot point) at the other end portion24B side. At a middle of the rocker arm 24, a pressed roller 24C isaxially supported to be freely rotatable. This pressed roller 24C isprotruding from an upper face of the rocker arm 24, and made to beabutted by a cam (not shown in the figure) provided at the cam shaft 6on the air intake side or the cam shaft 7 on the exhaust side.

(Lash Adjuster)

As shown in FIG. 4A and FIG. 4B, the lash adjuster 25 is equipped with amain body portion 26 in a cylindrical vessel shape, a plunger 27 of anapproximately tubular shape which is fit inside the main body portion 26and movable in an axial direction, a plunger spring 28 intermediatingbetween a bottom portion of the main body portion 26 and the plunger 27,and a check ball 29 for carrying out opening and closing of an opening27B formed at a center of a bottom portion 27A of the plunger 27 bybeing biased by the plunger spring 28.

In the main body portion 26 and the plunger 27, oil holes 26A and 27Care formed. Also, between an inner wall of the main body portion 27 andan outer wall of the plunger 27, an oil passage 25A for connecting theseoil holes 26A and 27C is formed. The oil hole 26A is connected to be incommunication with an oil passage for lash adjuster 31 to be describedlater. A space 30 in which the plunger spring 28 is arranged at thebottom portion of the main body portion 26 will function as a highpressure chamber. That is, this space 30 will become a high pressurechamber that is hard to be compressed even when a pressing force (shownby A in the figure) is received from the rocker arm 24 at a tip end ofthe plunger 27, by blocking the opening 27B of the bottom portion 27A ofthe plunger 27 with the check ball 29.

Also, as shown in FIG. 4B, in the case where the rocker arm 24 has movedto an upper side in the figure by receiving an influence from the airintake valve 20 or the exhaust valve 21 and the like, a pressure insidethe space 30 will be lowered and the oil will flow in from the oil hole26A (the flow of the oil is indicated by an arrow line B). Then, theplunger 27 will follow the other end portion 24B of the rocker arm 24 asindicated by an arrow C. At this point, the check ball 29 opens theopening 27B so that the oil will flow into the space 30. Then, in thecase where the rocker arm 24 swings and a pressing force is exerted onthe tip end of the plunger 27 from the other end portion 24B, becausethe opening 27B of the bottom portion 27A of the plunger 27 is blockedby the check ball 29, inside the space 30 will become a high pressure sothat it becomes difficult for the plunger 27 to be pushed down anyfurther.

(Main Oil Gallery, Oil Entry Passage and Oil Passage for Lash Adjuster)

FIG. 5 is a V-V line cross sectional view of FIG. 2. As shown in FIG. 5,in the cylinder head 3, a main oil gallery 32 is formed. This main oilgallery 32 is in communication with an output side of the oil pump 12shown in FIG. 1. It is made such that the oil ejected from the oil pump12 will be lead to the above noted lash adjuster 25 side and a camjournal not shown in the figure via the main oil gallery 32. As shown inFIG. 5, in the cylinder head 3, an oil entry passage 33 in communicationwith the main oil gallery 32 is formed. The oil entry passage 33 isconfigured from a first oil entry passage 33A formed along an up anddown direction which is in communication with an upper end portion ofthe main oil gallery 32, a second oil entry passage 33B formed along aleft and right direction of a vehicle body which is in communicationwith an upper end of the first oil entry passage 33A, and a third oilentry passage 33C formed along an up and down direction which is incommunication with the second oil entry passage 33B and which is openingat a joint surface 34 with the lower cam housing 4 of the first cylinderformation region 13 at an upper face of the cylinder head 3.

Also, in the cylinder head 3, oil passages for lash adjusters 31 areformed separately from the above noted oil entry passage 33. As shown inFIG. 4A, FIG. 4B and FIG. 8, the oil passages for lash adjusters 31 areequipped with first oil passages for lash adjusters 31A which areconnected to be in communication with the oil holes 26A of the lashadjusters 25 arranged at front and rear in the cylinder head 3. Also, asshown in FIG. 7, the oil passages for lash adjusters 31 are equippedwith second oil passages for lash adjusters 31B which have lower endportions in communication with the first oil passages for lash adjusters31A and which have upper end portions opening to a cam support surface(a bearing surface) of the lower cam housing 4A that is formedintegrally with the cylinder head 3. Note that, in the presentembodiment, the first oil passages for lash adjusters 31A are formed bythe drilling from a right side end face of the cylinder head 3. Then, asshown in FIG. 1, the openings of the drilling at the right side end faceof the cylinder head 3 are blocked by stoppers 40.

(First Upper Oil Passages)

Also, as shown in FIG. 6, in the cylinder head 3, a pair of first upperoil passages 36, with respective lower ends that are in communicationwith the first oil passages for lash adjusters 31A of the air intakeside and the exhaust side and respective upper ends that are opening atthe joint surface 34, are formed. These first upper oil passages 36 areset to be in communication with falling oil passages 37D to be describedlater.

(Lower Cam Housing)

As shown in FIG. 1, FIG. 5 and FIG. 6, the lower cam housing 4 isarranged to be extending along a vehicle front and rear direction, onthe joint surface 34 at one end portion (a right side end portion in avehicle left and right direction) of a cylinder array direction A (seeFIG. 2 and FIG. 3) in which the first cylinder 13A, the second cylinderand the third cylinder are arranged in a left and right direction, in anupper face of the cylinder head 3. This lower cam housing 4 is formed asa separate body from the cylinder head 3. Note that the other lower camhousing 4A is formed integrally with the cylinder head 3.

(Second Upper Oil Passage)

As shown in FIG. 9, FIG. 12 and FIG. 13, in the lower cam housing 4, asecond upper oil passage 37 is formed inside. The second upper oilpassage 37 comprises a rising oil passage 37A to be in communicationwith the third oil entry passage 33C formed in the cylinder head 3, aconnecting oil passage 37B in communication with a downstream end (anupper end portion) of the rising oil passage 37A, a horizontal oilpassage 37C in communication with a downstream portion of the connectingoil passage 37B, and falling oil passages 37D in communication with thefirst upper oil passages 36 at the joint surface 34, which are formedalong an up and down direction in such a way that they pass through thehorizontal oil passage 37C.

FIG. 10C is a bottom view of the lower cam housing 4. As shown in FIG.10C, the falling oil passages 37D are formed in such a way that theypierce in an up and down direction through respective ones of the bothend portions in a length direction of the lower cam housing 4. As shownin FIG. 10A and FIG. 10B, on the upper face of the lower cam housing 4,curved bearing portions 41, on which the cam shafts 6 and 7 of the airintake side and the exhaust side are axially supported, are formed. Asshown in FIG. 10A, on inner faces of these bearing portions 41, oilsupply grooves 42 that form oil passages in communication with thefalling oil passages 37D are formed.

As shown in FIG. 10B, at a center of the lower cam housing 4, theconnecting oil passage 37B is formed along a width direction (a left andright direction) of the lower cam housing 4. Note that, in the presentembodiment, this connecting oil passage 37B is formed by the drillingalong the width direction at the center portion of the lower cam housing4. Note that, as shown in FIG. 10B, an opening end portion of the secondupper oil passage 37B that is formed by the drilling is blocked by astopper 43.

As shown in FIG. 10C, at a center of a length direction in a bottom faceof the lower cam housing 4, the rising oil passage 37A is formed. Thisrising oil passage 37A can be formed by the drilling from a bottom faceside of the lower cam housing 4. Also, as shown in FIG. 6, inside thelower cam housing 4, the horizontal oil passage 37C is formed to beextending in the length direction. This horizontal oil passage 37C isformed by the drilling from one end face side in the length direction ofthe lower cam housing 4. As shown in FIG. 6, an opening at one end faceside in the length direction of this lower cam housing 4 is blocked by astopper 44.

FIG. 11A is a front view of the upper cam housing 5, and FIG. 11B is abottom view of the upper cam housing 5. As shown in FIG. 11A, in theupper cam housing 5, bearing portions 51 corresponding to the bearingportions 41 of the lower cam housing 4 are formed. As shown in FIG. 11B,on a bottom face of this upper cam housing 5, oil supply grooves 52 areformed at positions corresponding to inner faces of the bearing portions41 of the lower cam housing or positions for forming oil passages. Whenthis upper cam housing 5 is assembled on the lower cam housing 4, itbecomes possible to supply the oil as lubricant oil to the bearingportions 41 and 51, by the oil supply grooves 42 and 52.

(Assembling Structure for Lower Cam Housing and Upper Cam Housing)

A bottom face of the lower cam housing 4 is arranged to be abutting onthe joint surface 34 in the cylinder head 3. At this point, the thirdoil entry passage 33C on an upper face of the cylinder head 3 shown inFIG. 3 is set to be in communication with the rising oil passage 37A ofthe lower cam housing 4. Also, the first upper oil passages 36 formed atthe joint surface 34 on an upper face of the cylinder head 3 are set tobe in communication with the openings of the falling oil passages 37D ona bottom face of the lower cam housing 4. Then, as shown in FIG. 1 andFIG. 2, the lower cam housing 4 and the upper cam housing 5 are fixed bybolts 38 at plural locations with respect to the cylinder head 3.

(Effect and Operation)

In the oiling structure for engine of the present embodiment, it has thefollowing effect and operation in conjunction with the start of theengine 1. First, in conjunction with the start of the engine 1, the oilpump 12 is activated and supplies the oil inside the oil pan 11 to themain oil gallery 32 side. As shown in FIG. 5, the oil ejected to themain oil gallery 32 is entered into the first oil entry passage 33A, thesecond oil entry passage 33B and the third oil entry passage 33C. Also,the downstream end of the third oil entry passage 33C is opening at thejoint surface 34 of the cylinder head 3, and in communication with therising oil passage 37A of the lower cam housing 4. For this reason, theoil passing through the third oil entry passage 33C is entered toward anupper side at the rising oil passage 37A. Then, the oil passing throughthe downstream end (the upper end portion) of the rising oil passage 37Apasses through the connecting oil passage 37B, the horizontal oilpassage 37C and the falling oil passages 37D, and enters into the firstupper oil passages 36 that are in communication with the second upperoil passage 37 at the joint surface 34, and the first oil passage forlash adjuster 31A.

The oil entered into the first oil passage for lash adjuster 31A isentered into the lash adjuster 25 and the second oil passage for lashadjuster 31B. The lash adjuster 25 has an effect of canceling a valveclearance caused by the thermal expansion of the valve, by preventing ageneration of a clearance between the rocker arm 24 and the tip endportion of the plunger 27 due to the entry of the oil from the first oilpassage for lash adjuster 31A. Also, the oil entered into the second oilpassage for lash adjuster 31B is supplied as the lubricant oil betweenthe lower cam housing 4A that is formed integrally with the cylinderhead 3, and the cam shafts 6 and 7.

In the case where the engine 1 is stopped, the oil pump 12 is stopped,and there is a possibility for the oil inside the main oil gallery 32,the oil entry passage 33, the rising oil passage 37A, the connecting oilpassage 37B and the horizontal oil passage 37C to flow down to the oilpan 11 side. At this point, the oil inside the falling oil passages 37Din the second upper oil passage 37, the first upper oil passages 36, thefirst oil passages for lash adjusters 31A and the second oil passagesfor lash adjusters 31B will not flow down because an oil passageconnected to the oil pan 11 side does not exist on a lower side of theseoil passages. For this reason, the oil retained inside the falling oilpassages 37D, the first upper oil passages 36, the first oil passagesfor lash adjusters 31A and the second oil passages for lash adjusters31B will be supplied to the lash adjusters 25 when the engine 1 isre-started. For this reason, the remaining air inside the lash adjusters25 will not occur at a time of the re-start of the engine 1, and it ispossible to prevent the generation of the tappet sound and the adverseinfluence on the operations of the air intake valve 20 and the exhaustvalve 21.

Namely, in the oiling structure for engine according to the presentembodiment, by providing the first upper oil passages 36 and the secondupper oil passage 37 (the falling oil passages 37D) at positions higherthan the first oil passages for lash adjusters 31A, the oil remaining inthese oil passages can be supplied to the lash adjusters 25 at a time ofthe stopping of the engine 1. For this reason, in the presentembodiment, it is possible to prevent the oil inside the lash adjusters25 from becoming empty. In this way, it is possible to secure thesufficient oil in the lash adjusters 25 at a time of the re-start of theengine, and it is possible to prevent the generation of the noise(tappet sound) at a time of the re-start of the engine 1. Also, in thepresent embodiment, the lower cam housing 4 is a separate body from thecylinder head 3 at a time of forming the complicated second upper oilpassage 37 in the lower cam housing 4, so that it becomes easier tomanufacture, by the drilling and the like for example, and it ispossible to improve the productivity.

Also, in the present embodiment, the first oil passages for lashadjusters 31A comprise the (air intake side) oil passage for lashadjuster 31A that is in communication with the lash adjuster 25 to beused at the air intake side and the (exhaust side) oil passage for lashadjuster 31A that is in communication with the lash adjuster 25 to beused at the exhaust side. Then, in the present embodiment, the secondupper oil passage 37 is in communication with each of the first upperoil passage 36 on the air intake side and the first upper oil passage 36on the exhaust side. Because of such a structure in which the secondupper oil passage 37 is formed inside the lower cam housing 4, thesecond upper oil passage 37 can be connected surely at the joint surface34 with respect to the first upper oil passages 36 that are formed to beconnected to each of the oil passages for lash adjusters 31A of both theair intake side and the exhaust side. Because the lower cam housing 4can be fixed surely to the cylinder head 3, it is possible to preventthe oil leakage and the like. Also, in the present embodiment, becauseit suffices to fix the lower cam housing 4 to the cylinder head 3, it ispossible to improve the assembling performance.

Other Embodiments

In the above, the embodiment has been described, but the description andthe drawings that constitute a part of the disclosure of this embodimentshould not be construed as one that is limiting this invention. Fromthis disclosure, various alternative embodiments, implementations andoperation techniques will become apparent to those skilled in the art.

For example, in the above described embodiment, the rising oil passage37A, the connecting oil passage 37B, the horizontal oil passage 37C andthe falling oil passages 37D in the second upper oil passage 37 areformed to be perpendicular to each other, in order to make it easier tomanufacture each oil passage, but it is not limited to the abovedescribed structure, as long as it is a structure that has oil passagesfor leading the oil from the third oil entry passage 33C to the firstupper oil passages 36 at positions higher than the joint surface 34.

Also, in the above described embodiment, it is a configuration in whichthe rocker arm 24 that is swung by the cam is supported by the lashadjuster 25, but it is possible to apply the present invention even in aconfiguration in which the cam is directly abutting to the lash adjuster25.

The invention claimed is:
 1. An oiling structure for an engine,including a cylinder head of the engine having a combination of intakeand exhaust cam shafts, rocker arms adapted to swing in conjunction withrotations of said cam shafts, valves adapted to carry out opening andclosing operations in conjunction with swing motions of the rocker arms,and housing pairs, with each cam housing pair including a lower camhousing and an upper cam housing arranged to rotatably support the camshafts, wherein the rocker arms are each swingably supported at one-endthereof via hydraulic lash adjusters, and oil from an oil pump is guidedto the lash adjusters through an oil passage system including oilpassages for the lash adjusters formed in the cylinder head, wherein thelower cam housings include a lower cam housing formed as a separate bodyfrom the cylinder head and joined to the cylinder head, with a jointsurface region between the cylinder head and the lower cam housing, andthe oil passage system comprises: a set of first upper oil passagesformed inside the cylinder head, extending from the oil passages for thelash adjusters to the joint surface region, the first upper oil passageshaving upstream ends thereof opened at the joint surface region; an oilentry passage formed in the cylinder head, for entry thereto of oil fromthe oil pump, the oil entry passage having a downstream end opened atthe joint surface region; and a second upper oil passage formed in thelower cam housing to conduct oil to the joint surface region from abovethe joint surface region, the second upper oil passage having anupstream end thereof communicating with the oil entry passage at thejoint surface region, and downstream ends of the second upper oilpassage communicating with the set of first upper oil passages at thejoint surface region, wherein the lash adjusters include an intake lashadjuster and an exhaust lash adjuster, the oil passages for the lashadjusters include an intake side oil passage communicating with a firstoil hole at the intake lash adjuster, and an exhaust side oil passagecommunicating with a second oil hole at the exhaust lash adjuster, theset of first upper oil passages includes an intake side first upper oilpassage communicating with the intake side oil passage, and an exhaustside first upper oil passage communicating with the exhaust side oilpassage, and the downstream ends of the second upper oil passage includea first downstream end communicating with the intake side first upperoil passage, and a second downstream end communicating with the exhaustside first upper oil passage, and the oiling structure furthercomprising a first upwardly extending oil passage extending from theintake side oil passage to a first cam support surface of the lower camhousing supporting an intake cam shaft, and a second upwardly extendingoil passage extending from the exhaust side oil passage to a second camsupport surface of the lower cam housing supporting an exhaust camshaft.
 2. The oiling structure for an engine as claimed in claim 1,wherein said second upper oil passage is entirely arranged at positionshigher than said joint surface region.
 3. An oiling structure for anengine, including a cylinder head of the engine having a combination ofintake and exhaust cam shafts, rocker arms adapted to swing inconjunction with rotations of the cam shafts, valves adapted to carryout opening and closing operations in conjunction with swing motions ofthe rocker arms, and cam housing pairs, with each cam housing pairincluding a lower cam housing and an upper cam housing arranged torotatably support the cam shafts, wherein the rocker arms are eachswingably supported at one-end thereof via hydraulic lash adjusters, andoil from an oil pump is guided to the lash adjusters through an oilpassage system including oil passages for the lash adjusters formed inthe cylinder head, wherein the lower cam housings include a lower camhousing formed as a separate body from the cylinder head and joined tothe cylinder head, with a joint surface region between the cylinder headand the lower cam housing, and the lash adjusters include an intake lashadjuster and an exhaust lash adjuster, the oil passages for the lashadjusters include an intake side oil passage communicating with a firstoil hole at the intake lash adjuster, and an exhaust side oil passagecommunicating with a second oil hole at the exhaust lash adjuster,wherein the oil passage system further comprises: a pair of first upperoil passages formed in the cylinder head, extending from the intake sideand exhaust side oil passages to the joint surface region, respectively,the pair of first upper oil passages each having an upstream end openedat the joint surface region; an oil entry passage formed in the cylinderhead, for entry of oil from the oil pump, the oil entry passage having adownstream end opened at the joint surface region; a second upper oilpassage formed in the lower cam housing to conduct oil to the jointsurface region from above the joint surface region, the second upper oilpassage having an upstream end thereof communicating with the oil entrypassage at a first location in the joint surface region, and downstreamends of the second upper oil passage opened at second and thirdlocations spaced from the first location in the joint surface region;one of the first upper oil passages communicating with one of thedownstream ends of the second upper oil passage at the second location,the other of the first upper oil passages communicating with another ofthe downstream ends of the second upper oil passage at the thirdlocation, and wherein a spacing between the third location and the firstlocation is greater than a spacing between the second location and thefirst location, and wherein the other first upper oil passage has agreater passage length than the one first upper oil passage.